The present invention relates to a vehicle, or, mainly, automotive engine exhaust system in which a pair of front and rear cylinder banks of an engine, a crank shaft of which extends in a transverse direction of a vehicle body, are disposed in a longitudinal direction of the vehicle body, and in which a front exhaust pipe and a rear exhaust pipe which connect, respectively, to exhaust ports of the front cylinder bank and exhaust ports of the rear cylinder bank via exhaust manifolds are connected to a common collecting exhaust pipe at a collecting portion below the engine.
Conventionally, in an exhaust system for a so-called transverse V-type or horizontal opposed engine in which two front and rear cylinder banks are disposed in a longitudinal direction of a vehicle body with a crankshaft being disposed to extend transversely, a vehicle engine exhaust system is known in which a front exhaust pipe and a rear exhaust pipe which connect, respectively, to the front cylinder bank and the rear cylinder bank via exhaust manifolds are connected to a common collecting exhaust pipe at a collecting portion below the engine (for example, Japanese Utility Model Unexamined Publication Sho. 62-67921).
With the conventional vehicle exhaust system, however, the front exhaust pipe connected to the front cylinder bank is caused to extend toward the collecting portion below the engine from ahead of the engine, while the rear exhaust pipe connected to the rear cylinder bank is caused to extend toward the collecting portion below the engine from rearward of the engine, and the front and rear exhaust pipes are combined at substantially right angles at the collecting portion. This caused a problem that avoiding an interference of exhaust gas flows from the two exhaust pipes at the collecting portion is not possible, and as a result, interference noise of the exhaust gas flows is generated to constitute a cause of vehicle noise. Additionally, there was caused a problem that the interference of exhaust gas flows increases the exhaust resistance, which then reduces the exhaust gas flow rate, causing reduction in engine output.
The invention was made in view of the aforesaid situations, and a principal object thereof is to provide a novel vehicle engine exhaust system which can solve the aforesaid problems by improving the front and rear exhaust pipes, the common collecting exhaust pipe and the connecting portion of these exhaust pipes.
With a view to attaining the object, according to a first aspect of the invention, there is provided a vehicle engine exhaust system in which a pair of front and rear cylinder banks of an engine, a crank shaft of which extends in a transverse direction of a vehicle body, are disposed in a longitudinal direction of a vehicle body, and in which a front exhaust pipe and a rear exhaust pipe which connect, respectively, to exhaust ports of the front cylinder bank and exhaust ports of the rear cylinder bank via exhaust manifolds are connected to a common collecting exhaust pipe at a collecting portion below said engine. In the exhaust system, end portions on the collecting portion side of the front exhaust pipe and the rear exhaust pipe are arranged side by side in the same direction so as to be connected to the common collecting exhaust pipe, whereby exhaust gases flowing through the front and rear exhaust pipes are allowed to flow into the common collecting exhaust pipe in the same direction. According to the feature of the first aspect of the invention, it is possible to combine the exhaust gas flows from both the exhaust pipes at the collecting portion so as to flow in the same direction, whereby when compared with the conventional exhaust system, the interference of the exhaust gas flows can be reduced remarkably, thereby making it possible to solve the problems of generation of interference noise by the interference of the exhaust gas flows and reduction in the engine output.
In addition to above, in the first aspect of the present invention, the front exhaust pipe and the rear exhaust pipe are caused to extend downwardly from the exhaust manifolds, respectively, wherein the front exhaust pipe and the rear exhaust pipe are routed to below the engine by flexing the front exhaust pipe rearward of the engine and the rear exhaust pipe forward of the engine, whereafter either or both of the front exhaust pipe and the rear exhaust pipe are flexed again so that the ends on the collecting portion side of the two exhaust pipes are arranged side by side in the same direction so as to be connected to the common collecting exhaust pipe, and wherein mating faces which confront each other are formed, respectively, on sides of the front and rear exhaust pipes which are adjacent to each other, the mating faces being inclined relative to a plane passing through centers of the two front and rear exhaust pipes.
According to the first aspect of the invention, it is possible to reduce the likelihood that the thermal expansion of the exhaust pipes acts along the mating faces of the exhaust pipes as a force for causing a deviation between the mating faces, thereby improving substantially the fastening force at the collecting portion of the exhaust pipes and the strength of the constituent components at the collecting portion.
Furthermore, in the above-mentioned structure according to the present invention, it is preferable that the ends on the collecting portion side of the front exhaust pipe and the rear exhaust pipe are formed so as to have a cross section of a semi-circular shape, respectively, whereby flat face portions of the semi-circular end portions are made to function as the mating faces so that the end portions on the collecting portion side of the two exhaust pipes are arranged side by side in the same direction to thereby be connected to the common collecting exhaust pipe having a cross section of a circular shape, and wherein a ring member is provided upstream of a connecting portion between the end portions on the collecting portion side of the front and rear exhaust pipes and the common collecting exhaust pipe which is adapted to fit on an outer circumference of the end portions on the collecting portion side of the front and rear exhaust pipes so as to integrally hold the end portions on the collecting portion side.
According to the above-mentioned feature, it is possible to reduce the force acting on the connecting portion of the ends on the collecting portion side of the front and rear exhaust pipes with the common collecting exhaust pipe for causing a deviation between the front and rear exhaust pipes along the mating faces, as a result of which the strength and durability of the connecting portion can be improved.
Moreover, in the above-mentioned structure, it is further preferable that the outer circumference of the end portions on the collecting portion side of the two exhaust pipes and the ring member are welded together at portions of a fitting portion where the ring member fits on the front and rear exhaust pipes which do not intersect with extensions of the mating faces of the two exhaust pipes.
According to this structure, it is possible to alleviate the increase in stress at the ends of the front and rear exhaust pipes and ring member at the portion where the extensions of the mating faces of the two exhaust pipes and the ring member intersect with each other, whereby the reduction in strength and durability of the two exhaust pipes and the ring member can be suppressed minimally when the ring member and the outer circumference of the ends of the exhaust pipes are welded together.
The above-mentioned object can also be achieved by a vehicle engine exhaust system wherein a pair of front and rear cylinder banks of an engine a crank shaft of which extends in a transverse direction of a vehicle body are disposed in a longitudinal direction of the vehicle body. The vehicle engine exhaust system according to the present invention, comprises:
a front exhaust pipe connected to a front exhaust port of the front cylinder bank via a front exhaust manifold;
a rear exhaust pipe connected to a rear exhaust port of the rear cylinder bank via a rear exhaust manifold;
a common collecting exhaust pipe connected to both of the front and rear exhaust pipes at a collecting portion substantially disposed below the engine; and
a ring member integrally holding end portions of the front and rear exhaust pipes.
The end portions of the front and rear exhaust pipes which are located closer to the collecting portion are arranged side by side in the same direction so as to be connected to the common collecting exhaust pipe, whereby exhaust gases flowing through the front and rear exhaust pipes are allowed to flow into the common collecting exhaust pipe in the same direction. The end portions of the front and rear exhaust pipes which are located closer to the collecting portion are formed to have a cross section of a semi-circular shape respectively. The ring member is disposed upstream of the connecting portion defined by the end portions of the front and rear exhaust pipes and the common collecting exhaust pipe